1. Field of Invention
This invention relates to improvements in frictionally driven roller type transfer apparatus in which a pallet is stationary when the crossing angle between the axes of rotation of a driven roller and a driving shaft is zero, and the pallet may be driven when the angle is greater than zero.
2. Description of Prior Art
Conventionally, air cylinder type driving is utilized for moving a pallet to and fro, which has a drawback that its stroke is short and speed adjustment is difficult.
In Japanese Patent Laid-open Application No. 81562/1985, a pallet transfer apparatus is disclosed, which is, in the similar manner as the present invention, frictionally driven by a roller which is pressed against a driving shaft with a crossing angle between the axes of rotation. The one-way driving shaft in this case extends in the direction of the travel of the pallet. However, this prior art device is an automatic-turn type; and accordingly, a pallet cannot stop stably; and the accuracy of the stop position is rather poor. One way for solving this problem is to provide separate driving shafts for driving a pallet to and fro respectively; but such an alteration would render the whole structure of the transfer apparatus much complicated. Moreover, in prior art devices of this sort, it has not been possible to stop a pallet at intermediate positions.
In the next place, in a gyratory mechanism of the driven roller mounted in a pallet transfer apparatus of this sort, it has been conventional to dispose a coil spring for the purpose of urging the driven roller, which is frictioanlly driven by the peripheral surface of the driving shaft, to its zero position. However, in a case where the driven roller is urged to its zero position by means of such a coil spring, the zero position which should represent the stationary condition of the pallet is likely to become unstable; and accuracy of the stop position cannot be good.